Clear and concise description of the problem

Currently vitest fails a test run if it detects an unhandled rejection having been thrown:

Vitest caught 1 unhandled error during the test run.
This might cause false positive tests. Resolve unhandled errors to make sure your tests are not affected.

However, sometimes this is a desireable behaviour, especially when we are testing global unhandled rejection handlers.

Suggested solution

Several options are possible:

• Only report as a problem unhandled rejections that were not handled during the test execution (e. g. if there is no `process.on('unhandledRejection' handler that would consume the event);
• Make it possible to mark tests as expecting the unhandled rejections (e. g. syntax similar to expect.assertions(1) - expect.unhandledRejections(1))

Alternative

No response

Additional context

No response

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.